This invention relates to an improved method of and apparatus for drilling oil and gas wells using a mud motor.
When drilling with a mud motor reactive torque is a problem. High drilling rates and high weight on the bit causes the mud motor to stall, the bit to stop, and the drill string to rotate in the opposite direction due to torque build up in the drill string, and mud motor failure all caused by reactive torque, and torsional loads on the drill string. Therefore, it is an object of this invention to provide apparatus for and method of drilling that will balance reactive torque by drilling and underreaming simultaneously with a bit rotating in one direction and an underreamer rotating in an opposite direction.
Specifically, the apparatus of this invention includes a drill bit, a fluid powered motor connected to the bit for rotating the bit, an underreamer above the bit to increase the diameter of the well bore, and a gear box positioned between the bit and the underreamer for transmitting the reactive torque of the fluid powered motor to the underreamer to rotate the underreamer in a direction opposite that of the bit so that the torque rotating the bit is substantially the same as the torque rotating the underreamer to therefore create a balanced torque drilling system.
A hollow mandrel or torque tube 22 extends along the central axis of the apparatus from just above fluid powered motor 18 to just below top connection 25. Spline connection 23 between the upper end of the torque tube and bottom end 51 of connector 25 hold the torque tube from rotating around the central axis of the tool. The lower end of the torque tube is prevented from rotating by pins 36a and 36c that extend through pinions 28a and 28c, respectively, and the wall of housing 12. The torque tube, be it titanium and/or composite, serves to absorb shock torque especially from formation breaks, but also to permit rotating the drill string with the rotary table while drilling with a mud motor. This allows the tool to build angle with stabilizers when desired.
Therefore, it is an object and feature of this invention to provide a down hole drilling assembly to minimize or balance the reactive torque of a mud motor rotating a bit in one direction with an underreamer rotating in the opposite direction. This is accomplished by a gear box located between the mud motor and the underreamer. Specifically, the bit is turned by a mud motor, the upper end of the motor drives a reversing gear box that turns the underreamer in a direction opposite that of the bit. A torque tube or mandrel extends along the longitudinal central axis of the tool. The lower end of the torque tube is connected to the gearbox and to the gear box housing to hold lower housing section 12 in position to enclose and support the gear box and the mud motor. The torque tube also serves to supply drilling fluid under pressure to the mud motor through openings 26a, 26b and 26c in spacer 20 to rotate the bit connected to the output shaft of the mud motor. The torque tube is an axis guide for the underreamer to rotate about. Balancing the rotating members such as bit, stabilizer and underreamer is accomplished by grooved circular races 82 and 86 that contain a portion of high density small pellets in an oil/TEFLON fluid median. The pellets do not fill the grooves so that centrifugal force produced by the rotating tool causes balancing and increases mud motor life by decreasing bearing failure. FIG. 4 is an enlarged cross section view of one of the balancing grooves.
These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from this specification including the attached drawings, and appended claims.